/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.analysis;

import org.apache.lucene.util.ArrayUtil;

/**
 * Base utility class for implementing a {@link CharFilter}.
 * You subclass this, and then record mappings by calling
 * {@link #addOffCorrectMap}, and then invoke the correct
 * method to correct an offset.
 */
public abstract class BaseCharFilter extends CharFilter {

    private int offsets[];
    private int diffs[];
    private int size = 0;

    public BaseCharFilter(CharStream in) {
        super(in);
    }

    /** Retrieve the corrected offset. */
    @Override
    protected int correct(int currentOff) {
        if (offsets == null || currentOff < offsets[0]) {
            return currentOff;
        }

        int hi = size - 1;
        if (currentOff >= offsets[hi])
            return currentOff + diffs[hi];

        int lo = 0;
        int mid = -1;

        while (hi >= lo) {
            mid = (lo + hi) >>> 1;
            if (currentOff < offsets[mid])
                hi = mid - 1;
            else if (currentOff > offsets[mid])
                lo = mid + 1;
            else
                return currentOff + diffs[mid];
        }

        if (currentOff < offsets[mid])
            return mid == 0 ? currentOff : currentOff + diffs[mid - 1];
        else
            return currentOff + diffs[mid];
    }

    protected int getLastCumulativeDiff() {
        return offsets == null ? 0 : diffs[size - 1];
    }

    protected void addOffCorrectMap(int off, int cumulativeDiff) {
        if (offsets == null) {
            offsets = new int[64];
            diffs = new int[64];
        } else if (size == offsets.length) {
            offsets = ArrayUtil.grow(offsets);
            diffs = ArrayUtil.grow(diffs);
        }

        offsets[size] = off;
        diffs[size++] = cumulativeDiff;
    }
}
